The present invention is a further development of the device for forward feeding of product carriers described in the Swedish patent SE 509402. The said document describes a device for forward feeding of product carriers movably resting on a main rail onto which branches are arranged for feeding product carriers in to and feeding product carriers out from the main rail. The product carriers are transported by an endless belt. Guiding means are used in order to ensure that the product carriers are securely transported along the main rail and to ensure that the product carriers do not derail from the main rail. In order for the product carrier to be able to be transported from the main rail to a feeding-out rail or from a feeding-in rail to the main rail, it is necessary that the guiding means allows that transfer is made at the branches of the feeding-in rail and the feeding-out rail respectively. In the embodiments of the device shown in SE 509402 that are on the market a beam profile is arranged, which integrally comprises the support surfaces of the main rail on which the product carrier rests during transport, and also the guiding means. The guiding means is formed as an upwardly protruding flange between the said support surfaces. The product carrier's wheels are placed on each side of the flange wherein derailing of the product carrier is hindered. When the branches have been arranged according to prior art, the beam profile with support surfaces and guiding rail has been cut and a switch device has been arranged for feeding in and feeding out. Since the guiding rail according to the prior art has been integrally formed with the main rail as part of one and the same beam, the beam forming both guiding rail and main rail has been cut at the position where a switch is to be arranged. As a consequence of the beam being cut, a transport device according to the prior art will be weakened in the area of the switch. In order to ensure to that there is enough bending stiffness for the supporting beam unit in the area of the switch, the transport device in accordance with prior art has been equipped with an upper load-bearing beam structure B presenting a relatively large height H in order to ensure that there is enough bending stiffness (see FIG. 1). The construction according to prior art also gives additional costs when a production flow shall be changed by further addition of switches being mounted to an existing track or in the case where the position of the switch has to be moved for any reason.